The present invention relates to an electronic map apparatus and a method of displaying an electronic map.
In an onboard navigation apparatus mounted on a vehicle, a map is displayed on a display unit in accordance with map data read out from a memory such as a CD-ROM. Typically, there is provided a function to draw lines along longitude and latitude lines, superposing the lines on the map at predetermined intervals to form a shape resembling a checkerboard as shown in FIG. 6A.
Thus, by using this drawing function, for example, it is possible to know an approximate geographical distance between the present position of the vehicle and a destination of the vehicle such as a location or a building.
In addition, electronic map viewer application software executed on a personal computer, for example, includes a function for displaying a scale showing a geographical distance outside the frame of a displayed map. By using this distance scale, a geographical distance can also be determined.
In the case of such a display method, however, in an attempt to know the approximate geographical distance between the present position of the vehicle and the destination of the vehicle such as a location or a building while driving the vehicle, it is difficult to know the geographical distance instantaneously. Particularly, it is more difficult to know a geographical distance in a direction slanting with respect to a longitude or latitude line.
FIG. 6A is a diagram showing a map in a top view. In general, however, an onboard navigation apparatus mounted on a vehicle also includes a function to convert original map data into a map displayed in a perspective view as shown in FIG. 6B.
On a map displayed in a perspective view, a unit-length distance varies from position to position as well as from direction to direction. It is thus much more difficult to intuitively and speedily know an actual geographical distance.